1. Field of the Invention
The present invention relates to a valve driving apparatus for performing variable control of a lift amount, lift timing and an actuated angle in accordance with an accelerator opening in an internal combustion engine in a motorcycle, an automobile or the like.
2. Description of the Related Art
In this type of internal combustion engine, combination of a variable phase and cam switching begins to appear recently, and thereafter, a method with use of a three dimensional cam for making the actuated angle and the lift amount continuously variable is proposed. For example, there is a method in which a follow-up mechanism for a change in a contact angle is provided at a top portion of a direct striking type cylinder tappet, and by sliding the three-dimensional cam in an axial direction, the valve lift amount is made continuously variable.
This type of three-dimensional cam is provided extensively with a cam portion gradually inclined in a longitudinal direction (axial direction of a camshaft), and is formed in a shape to continuously change the valve lift amount. In this case, setting is made such that a cam operation angle and lift timing are changed synchronously with cam height, namely, the cam operation angle becomes larger as the valve lift amount becomes larger, and the lift timing of the valve is capable of being changed. By moving such a cam along the camshaft, the lift amount, the actuated angle and lift timing of an intake valve can be controlled to be continuously variable via the valve lifter including the tappet.
By applying such a three-dimensional cam to, for example, the intake valve at an intake side, a throttle valve to form a mixture is eliminated, and a so-called non-throttle valve engine can be realized. Incidentally, when fine adjustment of the valve lift amount is performed, or tuning of cylinders is performed in a multi-cylinder engine, fine adjustment of a tappet guide is performed in a slide direction of the cam with use of, for example, an eccentric cam in the prior art.
On the occasion of fine adjustment of the valve lift amount (intake boost) or tuning of the cylinders as described above in the above prior art, fine adjustment or tuning is performed with a cylinder head cover being removed from a cylinder head. In this case, if fine adjustment is performed for an intake boost with the engine being rotated, lubricant oil easily scatters, and therefore it is necessary to prevent scattering of oil with use of a special tuning cover. When tuning is performed without rotating the engine, it is necessary to use a device for measuring the valve lift amount in the cylinder head unit.
Further, on the occasion of maintenance of the cylinder head unit in a maintenance service and the like after manufacture and shipment, there is no other way except for taking the method for preventing scattering of oil by removing the cylinder head cover and using the tuning cover, and tuning cannot help being performed at much expense in time and effort.